1. Field of the Invention
The present invention generally relates to a wired signal receiving apparatus.
2. Description of Related Art
Along with the advancement of our society, information exchange has become a very important part in our daily life. The wired signal transmission technique is one of the most commonly used and mature techniques, and which offers higher stability and higher security compared to the wireless signal transmission technique.
However, a conventional wired signal transmission system has some disadvantages in the fast transmission of large quantity of data. FIG. 1 illustrates a conventional wired signal transmission system 100. The wired signal transmission system 100 includes a signal transmitting apparatus 110, a signal receiving apparatus 120, and a transmission line 130 coupled in between for transmitting signals. In order to allow the wired signal transmission system 100 properly function, the currents provided by the current sources IS, IL, and IM have to meet the condition of IL>IM>IS, and preferably, IM=(IL+IS)/2.
When the signal transmitting apparatus 110 is about to transmit a data of logic low level, the current source IL is connected to the transmission line 130, and a current is produced on the resistor R1 of the signal receiving apparatus 120, wherein the current has value IL−IM and which flows to the first input terminal of the amplifier OP1. This current makes the voltage on the first input terminal of the comparator CMP1 to be lower than the voltage on the second input terminal of the comparator CMP1 therefore allows the output signal OUT to have the logic low level. Contrarily, when the signal transmitting apparatus 110 is about to transmit a data of logic high level, the current source IS is connected to the transmission line 130, and a current is produced on the resistor R1 of the signal receiving apparatus 120, wherein the current has a value IM−IS and which flows to the output terminal of the amplifier OP1. This current makes the voltage on the first input terminal of the comparator CMP1 to be higher than the voltage on the second input terminal of the comparator CMP1 therefore allows the output signal OUT to have the logic high level.
The signal transmitting apparatus 110 can work properly only when all the features of the receiving device thereof match all the features of the transmitting device thereof. If mismatched features (for example, the condition of IL>IM>IS is not met, IM is slightly smaller than IL, or IM is slightly larger than IS) are caused by changes in the ambient conditions of the signal receiving apparatus 120 and the signal transmitting apparatus 110 or process variations when the apparatuses are manufactured, the signal transmitting apparatus 110 may lose some timing margin, and accordingly the duty cycle of the output signal RX_OUT may not be 50%. As a result, the wired signal transmitting apparatus 110 may not be able to work properly for transmitting data in high frequency.